Glass



Patented Apr. 29, 1941 GLASS Rudolf Schmidt, Weisswasser, Oberlausitz,and

Walter Hanlein, Berlin-Spandau, Germany, assignors to General ElectricCompany, a corporation of New York 1 No Drawing. Application February 8.1938, Serial No. 189,452. In Germany February 18, 1937 3 Claims.

The present invention relates to the glass art generally and moreparticularly the invention relates to glass compositions useful ascontainer glasses for gaseous electric discharge lamp devices thegaseous atmosphere of which consists of or comprises a chemically activemetal vapor, such as sodium vapor.

Glasses of this type are now known in the art and one such glass is aboro-silicate glass containing about to 25% of silica, an appreciableamount of boric anhydride, and other usual glass constituents, such asalkalies, alkaline earths and aluminium oxide. Such glasses aresuccessfully used in sodium vapor discharge lamps in which the currentinput is such that the container temperature is about 240 C. When thecurrent input is increased to raise the container temperature to about300 C. the glass takes on a brownish tint which is undesirable. Attemptsto solve this problem by increasing the boric anhydride content of theglass to above 60% and by reducing the silica content to about 4 to 9%have been made. While such glass compositions do not become brownishwhen used as a container glass for an alkali vapor lamp operating atsuch elevated container temperatures the manufacture of lamp containerscomprising such a glass is expensive and complicated due to the factthat the glass is very hygroscopic. Small amounts of moisture, such asthat introduced into the lamp container from the gas flame during themanufacture thereof are suflicient to start weathering of the glasswhich appears as a bluish-grey veil during the operation of a sodiumvapor discharge device. The resistant glass rapidly becomes moreabsorbent of the light emitted by the vapor discharge and the lamp has avery short life.

The object of the present invention is to provide a glass compositionwhich is resistant to hot, ionized, alkali metal vapor, such as sodiumvapor, and which is non-hygroscopic. Another object of the invention isto provide a non-hygroscopic, alkali vapor resistant glass having acoefiicient of expansion approximating that of the usual non-alkalivapor resistant glasses, such as the soda glasses, used generally in thelamp art as container glass. Still further objects and advantagesattaching to the device and to its use and operation will be apparent tothose skilled in the art from the following particular description.

We have discovered that a glass consisting of about 20 to 30% boricanhydride (B203), about 20 to 30% alumina (A1203), about 4 to 9% silica(S102), about 30 to 40% alkaline earths and about 6 to 10% alkalies hasthe desirable alkali vapor resistant properties described above and is anon-hygroscopic glass.

Preferably the glass of the present invention is used as the inner layerof a two layer glass container the outer layer of which consists of asoda glass having a coefficient of expansion of about to 10- usedextensively at present as a container glass for electric lamp devicesand which is subject to attack by hot, ionized alkali metal vapor. Thisglass has the following composition in percentages by weight:

Per cent Silica (S102) 69.5 Alumina (A1203) 2.0 Potassium oxide (K20)1.0

Sodium oxide (NazO) 16.5

Calcium oxide (CaO) 5.5 Magnesium oxide (MgO) 3.5 Barium oxide (BaO) 2.0

When a glass having the above composition is used as the outer layer ofthe container the inner layer preferably consists of an alkali vaporresistant, non-hygroscopic glass having the following composition inpercentages by weight:

. Per cent Silica (SiOz) 5.0 Boric oxide (B203) 25.0 Alumina (A1203)25.0 Barium oxide (BaO) 36.5 Sodium oxide (NazO) 6.0 Potassium oxide(K20) 2.5

Since both of the above glasses are soft glasses the current leads andthe machines and methods used in the fabrication of incandescent lampscan be used in the manufacture of alkali vapor discharge lamp devices.

A lamp container having the above structure is useful for vapordischarge lamps generally and particularly forsuch lamps operating atelevated container temperatures similar to those described in co-pendingapplication Serial Number 127,500, filed February 24, 1937, now U. S.Patent 2,161,824.

What we claim as new and desire to secure by Latters Patent of theUnited States, is:

1. A glass resistant to hot, ionized alkali metal vapor when at atemperature of 300 0., said glass being capable of fusion with anon-alkali vapor resistant, soft soda glass having a coefficient ofexpansion of about 80 to 90 10" to form a two layer glass container foran alkali vapor discharge lamp, said resistant glass consisting of aboutto boric anhydride (B202), about 20 to 30% alumina (A1203), about 4 to9% silica (S102), about 30 to alkaline earths and about 6 to 10%alkalies.

2. A glass having the following composition:

Per cent Silica (S102) 5.0 Boric oxide (B203) 25.0 Alumina (A1203) 25.0Barium oxide (BaO) 36.5 Sodium oxide (Na20) 6.0 Potassium oxide (K20)2.5

3. A glass resistant to hot, ionized alkali metal vapor when at atemperature of 300 0., said glass being capable of fusion with anon-a1kaliva por resistant, soft soda glass having a coefiicient ofexpansion of about to 10- to form a two layer glass container for analkali vapor dls charge lamp, said soda glass having the followingcomposition:

Per cent Silica (S102) 69.5 Alumina (A1203) 2.0 Potassium oxide (K20)1.0 Sodium oxide (Na20) 16.5 Calcium oxide (CaO) 5.5 10 Magnesium oxide(MgO) 3.5 Barium oxide (BaO) 2.0

15 40% alkaline earths and about 6 to 10% alkalies.

RUDOLF SQl-IMIDT. WALTER I-IANLEIN.

